Optical fibers are commonly coupled to one another by attaching a terminus to the stripped end of each optic fiber cable. The tip of each optic fiber is lapped flush with the tip of a ferrule of the terminus. The tips of the ferrules and fibers are aligned within a precision alignment sleeve so the tips of the two fibers abut one another. In practice, the tips of the fibers are slightly eccentric to the axis of the ferrules (e.g. by perhaps 3 microns for a single mode fiber of 9 microns diameter), and the tips lie in planes that are not exactly perpendicular to the ferrule axes. This results in an insertion loss, which is the loss of light intensity due to the light having to pass between the tips of two imperfectly abutting fibers.
The insertion loss can be reduced by rotating one terminus and its corresponding optical fiber, to different positions about the terminus axis and measuring the insertion loss at each position. For nonpolarized systems, a terminus position within about 30° of the ideal terminus position produces approximately the lowest insertion loss. For systems where the light is polarized, a rotational position angled even a few degrees from the position of minimum insertion loss, can result in a significantly greater insertion loss than at the best position. Since a terminus occasionally has to be removed from its housing, as to clean its tip, it is desirable that any means for fixing the orientation of the terminus enable removal of the terminus and its reinstallation at the optimum position.
Optical fiber connectors that connect a plurality of pairs of optical fibers, are generally constructed with their terminus-receiving passages closely spaced, and often at a standard spacing so the overall size of the connector is a minimum. It is desirable that any means for fixing the orientation of the terminus, enable the same spacing between passages as when no means is provided to fix the terminus orientation.